In the patent literature, there are many patents which deal with broadcast mechanisms. Some broadcast mechanisms are not implemented by hardware. For instance, U.S. Pat. No. 4,818,984 to S. J. Chang et al. issued on Apr. 4, 1989, describes a broadcast mechanism implemented in software.
Switching networks are different from busses and local area networks (LANs). For instance, it would be recognized that U.S. Pat. No. 4,926,375 to F. L. Mercer et al. issued on May 15, 1990, relates to a broadcast mechanism implemented over a multi-drop bus. U.S. Pat. No. 4,706,080 to W. D. Sincoskie issued on Nov. 10, 1987, describes a broadcast mechanism implemented over several multi-drop busses; as does U.S. Pat. No. 4,855,899 to S. D. Presant issued on Aug. 8, 1989; as also does the publication by IBM in the TECHNICAL DISCLOSURE BULLETIN; IBM TDB Vol. 30, No. 1, 6/87 pg 72-78, POLL ACTUATED MULTIPLE ACCESS TECHNIQUE FOR BROADGATHERING SYSTEMS.
There are several patents which describe broadcast mechanisms for LANs. U.S. Pat. No. 4,754,395 to B. P. Weisshaar et al. issued on Jun. 28, 1988, describes a broadcast mechanism implemented over a serial, loop-connected LAN. U.S. Pat. No. 4,835,674 to R. M. Collins et al. issued on May 30, 1989, describes a broadcast mechanism implemented over multi-drop busses tied to LANs and broadcasting over the entire set-up.
Some broadcast mechanisms are designed for synchronized, multiplexed time slot, bit oriented networks, as represented by U.S. Pat. No. 4,897,834 to J. R. Peterson et al. issued on Jan. 30, 1990, and others such as U.S. Pat. No. 4,766,592 to E. Baral et al. issued on Aug. 23, 1988, describe a broadcast mechanism implemented over a synchronized, multiplexed time slot, telephone line hook-up. IBM TDB Vol. 22, No. 12, 5/80 pg 5450-52, DISTRIBUTED STAR NETWORK WITH UNROOTED TREE TOPOLOGY describes a broadcast mechanism implemented over an unrooted tree network which uses synchronous transmissions and packet switching.
Other mechanisms are designed for transmission lines. U.S. Pat. No. 4,935,866 to R. Sauvajol et al. issued on Jun. 19, 1990, describes a broadcast mechanism implemented over a synchronous, transmission line, communication link. U.S. Pat. No. 4,941,084 to M. Terada et al. issued on Jul. 10, 1990, describes a broadcast mechanism implemented over a transmission line, loop interconnect arrangement. U.S. Pat. No. 4,815,105 to S. Bottoms et al. issued on Mar. 21, 1989, describes a broadcast mechanism implemented over a transmission line, telephone line type interconnect arrangement. While telephone switches have employed crossbar switches, generally they do not use parallel connect crossbar switches.
There is a need for improved switching network approaches using parallel connect crossbar switches (a non-loop or transmission line approach) for circuit switching networks for asynchronous, dedicated path (not time slotted), byte-wide parallel direct connect switching. The present broadcast mechanism relates to multi-stage networks.
Some prior multi-stage switching networks have been developed. U.S. Pat. No. 4,956,772 to P.M. Neches issued on Sep. 11, 1990, provided a buffered packet synchronous switch. This complex single serial interface line switch requires data recovery capabilities. It needs a complex priority determination built into each switch stage and brings the broadcast command bits into the switch serially. Another packet switch which relates to a multi-stage switching network is U.S. Pat. No. 4,701,906 to M. N. Ransom et al. issued on Oct. 20, 1987. It also is a buffered synchronous packet switch and provides for a handshaking interface. It brings the broadcast command bits into the switch serially, and the complex switch also requires data recovery capabilities. It is a single serial interface and appears not to have considered the need for an asynchronous byte-wide parallel interface for broadcast applications.
Broadcasting a message from one device to N devices through a multi-stage network composed of BUFFERED switching devices is a relatively simple task. At each switch the message is fanned-out to all the switch outputs by inserting it into a queue (ordered buffer) associated with each output. The transmitter of the broadcast message does not have to concern itself with contention at each switch output (i.e., the output being busy transmitting previously initiated messages). If the output is busy, the broadcast message merely goes into a queue of messages waiting to use the output and eventually will get its turn and the broadcast message will propagate slowly through the network. However, there are three drawbacks to using buffered networks. They are usually relatively slow; there is the problem of not knowing when the broadcast will arrive, and certainly it will arrive at vastly different times at the various receiving devices; and buffered networks usually require synchronization across all transmitting and receiving devices as well as the network switches themselves. Synchronous systems are finding it more and more difficult to meet the ever-increasing communication demands of modern parallel processing systems; they are just not fast enough to keep pace with the rapidly increasing computer clock rates, and thus they are becoming a high risk problem.
On the other hand, UNBUFFERED asynchronous networks can provide greatly improved speed at a much lower complexity, risk, and cost. However, one of the problems usually inherent with unbuffered networks is that they cannot BROADCAST messages (i.e. send messages over the switching network from one device to all the devices attached to the network).
In addition, there is arising a new need in the parallel processing field to send a multi-cast message from one device to a specific set of devices attached to the network but not to all the devices as broadcast does. In general multi-cast is an even harder function to implement through an unbuffered switching network than is broadcast.